In general, axial gap rotating electrical machines are comprised of : a pair of rotor having two circular disks provided on the respective opposite surfaces thereof with permanent magnets and a shaft coupling the circular disks together, located in the centers thereof; a stator made up of multiple cores and coils to which the permanent magnets are opposed with a gap in between; and a pair of bearings rotatably supporting both ends of the shaft and bearing holders holding them.
As an example of axial gap rotating electrical machines in which a rotor and a stator are arranged opposite to each other in the direction of the central axial line thereof, there is that described in Patent Document 1 (JP-A-5-316709).
This axial gap rotating electrical machine is formed as follows: Independent electromagnetic steel plate cores with a coil wound thereon are positioned and arranged in the circumferential direction. They are set in dies with insulating material placed between coils and integrally molded with molding resin or by varnishing to form the stator of the rotating electrical machine. Thereafter, a rotor is installed through two bearings. At the last, they are placed in a housing to fix the stator.
As technologies related to the manufacture of this axial gap rotating electrical machine, there are known those described in Patent Document 2 (JP-A-2006-94664) and Patent Document 3 (JP-A-2008-35599).
In the manufactured axial gap rotating electrical machines having the above configuration, it is necessary to accurately place each component part such as a stator core. If variation is produced in the position or disposition of stator cores, the cogging torque of the axial gap rotating electrical machine will become larger than a calculated value and this will increase vibration and noise.
In the technology in Patent Document 2 (JP-A-2006-94664), to accurately position cores, a positioning jig is used in the manufacturing process and an insulator is provided for insulating stator core and coils. In addition, molding dies are used. As a result, the scale of the manufacturing process step for resin-molding the stator is increased.
In the technology in, for example, Patent Document 3 (JP-A-2008-35599), multiple support members in such a shape that they are split along the inner circumference of a housing are provided in the circumferential direction in place of resin-molding the stator. To hold the support members and stator cores, engaging portions engaged with support portions in the circumferential direction are provided. In addition, recessed portions are provided for engaging the stator cores.
However, the structure disclosed in Patent Document 3 (JP-A-2008-35599) involves a problem associated with joining between the support members and the stator cores. The resin-molded stator reduces the mechanical strength of the joints. As the rotating electrical machine rotates, the joints are influenced by vibration and there is a possibility that a stator core is displaced. In high-speed rotation, especially, a problem of strength is prone to rise. Since the stator cores are provided with a recessed portion, the area opposed to magnets is reduced. Therefore, the flux linkage between the rotor magnets and the stator cores is reduced.
To sum up, the rotating electrical machine structures in the above patent documents involve problems associated with the accurate positioning of stator cores in the assembly of rotating electrical machines and the simplification of a manufacturing process. As a result, these technologies cannot contribute to the enhancement of the performance of rotating electrical machines as finished products.
The present invention has been made to solve the above problems. An object of the present invention is to provide an axial gap rotating electrical machine which can position stator cores accurately and simplify the manufacturing process.